1. Field
The present disclosure relates generally to the fabrication of composite structures and, more particularly, to a method and system for determining cumulative foreign object characteristics during fabrication of a composite structure.
2. Background
Composite structures for aircraft and other applications have been known for many years and can be fabricated in many different ways. One advantageous technique for fabricating composite structures is a fiber and tape placement process. According to conventional techniques, one or more ribbons of a composite resin material, also known as composite strands or tows, are laid down on a substrate by a material placement machine. The substrate may be a tool or mandrel, but may also be one or more underlying layers of composite material that have been previously laid down and compacted.
Conventional placement processes utilize a heat source in conjunction with a compaction roller to apply the ribbon or tow onto the substrate at the nip of the compaction roller. More particularly, the ribbon or tow of composite resin material and the underlying substrate are heated at the nip as the material placement machine moves across the substrate to increase the tackiness of the resin material while the resin material is being subjected to compressive force by the compaction roller to adhere a strip or course of the composite resin material to the substrate.
To form a composite structure, a plurality of courses of the composite material are laid down in a side-by-side manner to form a first layer or ply of composite material. A similar plurality of courses of composite material may then be applied to the surface of the first ply to form a second ply on the first ply. The process is repeated until a desired number of plies have been formed one above another. In this way, a composite structure can be fabricated course-by-course and ply-by-ply until the composite structure is completed.
As the courses of composite material are laid down by the material placement machine, foreign objects and debris (FOD) may accumulate on the surface of the composite structure. FOD may include, for example and without limitation, resin balls, fiber wads, and pieces of backing material.
When FOD occurs during the laying down of a course, it is desirable that the FOD be detected and removed from the surface of the ply being formed before the next ply is formed as the FOD will otherwise become embedded between adjacent plies which may be undesirable. Failure to remove FOD may also result in bulges and other inconsistencies in the final composite structure. It is desirable therefore, to be able to detect the presence of FOD in real time while the courses are being laid down to form a ply so that they may be removed before a subsequent ply is formed.
There are current systems that are able to detect discrete foreign object occurrences so that they may be removed. It would be desirable, however, to also make cumulative determinations with respect to the detection of FOD. For example and without limitation, it would be desirable to make cumulative determinations with respect to the total number of FOD detected during fabrication of a composite structure or with respect to the total number of each of various types of FOD that are detected during fabrication of the structure. Such information may be useful in identifying problem areas with regard to the material placement machine or the overall composite structure fabrication process to enable appropriate adjustments or changes to be made to reduce the occurrence of such foreign objects and for other reasons.